Printed circuit board or card thermal mass design

ABSTRACT

A multi-layer printed circuit board or card including at least one passage in at least one of the layers of the circuit board or card for preventing the diffusion of heat throughout the circuit board or card during the securing or removal of components in plated through holes in the circuit board or card by the heating of the plating material to a temperature above a melting point of the plating material.

FIELD OF THE INVENTION

The invention relates generally to printed circuit boards and cards, andmore particularly to an improved printed circuit board design enhancingheat flow through the circuit board to heat traps or thermal ventsthereby preventing heat build up in the circuit board or card.

BACKGROUND OF THE INVENTION

During rework of a circuit board, the process of removing componentsfrom the board, two conflicting goals must be accomplished. First, theproper heat must be maintained to allow the solder securing thecomponents to the circuit board to reach and remain at the reflowtemperature. Secondly, it is necessary to prevent the applied heat fromdispersing through the circuit board to adjacent components and causingpotentially damaging stress to the circuit board or card and componentsattached thereto.

It is common to mount complex electronic components on printed boards byinserting pins extending from components into plated through holes inthe circuit board and soldering them in place. The plated through holesnormally provide connections between the pins and conductive materialsituated at various levels of the circuit board or card.

As the number of components attached to the circuit board increases,both the number of pins and the number of times the board must be heatedto solder the pins in place increase. Therefore, during rework, a greatamount of heat is potentially applied to a circuit board or card.

As the circuit board increases in size and thickness, the total amountof copper and the number of planes common to a single via all contributeto insufficient soldering and the inability to rework an assembly.Further, the soldering process is adversely effected when tied planes ina circuit board or card, that is, planes in the circuit board or cardthat are electrically connected to the through hole, allow heat beingapplied to the plated through hole to escape into the internal planes ofthe circuit board. The escape of heat from the through hole reduces thethrough hole temperature to below the solder melting point resulting ininsufficient hole fill.

The draining of heat from the through hole is especially prevalent whentwo or more planes are common to a single through hole. This allows heatto escape into the internal planes of the circuit board or card from theplated through hole, thereby inhibiting the top surface of the carrierfrom reaching the solder reflow temperature. Thicker circuit boards thatdo not have common power planes also experience rework problems. It isalso essential that when heat is applied to the circuit board duringrework that the temperature not exceed the melting point of the materialused to form the circuit board. However, enough heat must be applied tothe solder to cause the solder to melt throughout the length of theplated through hole.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a new circuit boarddesign to prevent the above described problems. One modification tocircuit board design which may prevent overheating and damage to a highperformance card assembly during assembly and rework includes providingthermal venting means to the card structure. Alternatively, a lowinductance thermal relief design in the power plane may be used inconjunction with an optimum connection scheme traversing through all thelayers of the card. A third option for an improved thermal design formanufacturing high performance circuit board and card assemblies is tocreate a thermal network using power vias.

The present invention solves problems existing in the manufacturing ofhigh density, high performance card assemblies through the use ofmodifications to power plane connections by providing a multi-layerprinted circuit board or card including a plurality of power, ground,and insulating planes having a plurality of holes formed therethrough.The through holes have an electrically conductive material plated ontothe inside surface. At least one integrated chip or component isattached to the circuit board or card such that pins at least partiallymade of an electrically conductive material and attached to a surface ofthe chip or component extend into the plated through holes. The circuitboard or card comprises at least one passage in at least one of theplanes for preventing the diffusion of heat throughout the circuit boardor card during the securing or removal of the pins in the plated throughholes. The pins are secured by the heating of the plating material to atemperature above its melting point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a perspective view of a printed circuit board or cardincluding thermal vents according to one embodiment of the presentinvention thermal mass design.

FIG. 2 represents a perspective view of a printed circuit board or cardincluding thermal vents according to another embodiment of the presentinvention thermal mass design.

FIGS. 3a-g represent possible schemes for the placement of thermal ventsin a printed circuit board or card according to the present invention.

FIGS. 4a-e represent additional possible schemes for the placement ofthermal vents in a printed circuit board or card according to thepresent invention.

FIG. 5 represents an overhead cross-sectional view of a design forthermal vents according to one embodiment of the present invention.

FIG. 6 represents a cross-sectional view along line A--A of theembodiment of the present invention shown in FIG. 5.

FIG. 7 represents an overhead cross-sectional view of the thermal ventdesign shown in FIG. 5.

FIG. 8 represents an overhead cross-sectional view of an another designfor thermal vents according to another embodiment of the presentinvention.

FIG. 9 represents a cross-sectional view of a printed circuit board orcard including non-functional tie vias connected to the power planes ofa circuit board or card according to one embodiment of the presentinvention.

FIG. 10 represents a cross-sectional view of a printed circuit board orcard including non-functional tie vias connected to the power planes ofa circuit board or card according to another embodiment of the presentinvent ion.

FIG. 11 represents a partial overhead view of a printed circuit boardincluding heat trap vias placed about the periphery of a componentattached to a circuit board or card according to one embodiment of thepresent invention.

FIG. 12 represents an overhead view of a module attached to a circuitboard or card including heat trap vias showing the flow of heat throughthe circuit board or card according to the embodiment in FIG. 11.

FIG. 13 represents a close-up cross-sectional view of the circuit boardaccording to the embodiment of the present invention shown in FIGS. 11and 12.

FIG. 14 represents a perspective view of a component to be attached to acircuit board or card to be attached to a circuit board or cardaccording to one embodiment of the present invention shown in FIGS. 11,12, and 13.

FIGS. 15a-e represent various configurations of circuit boards withwhich various embodiments of the present invention may be used.

DETAILED DESCRIPTION OF VARIOUS AND PREFERRED EMBODIMENTS

Multi-layer circuit boards and cards are formed from multiple layers,some of which are made of electrically conductive material and some ofelectrically insulating material. A number of holes are formed incircuit boards and cards for the connecting of integrated circuits andvarious other components. The components may have pins extending fromtheir surface which are inserted into the holes in the circuit board orcard. The holes are coated, or plated, with electrically conductivematerial which is functionally connected to the component. Such holesare often referred to as plated through holes. The plating material onthe inside of the holes is selectively connected to the layers of thecircuit board or card.

Components are usually secured to a circuit board or card by causing theplating material in the plated through holes to be heated to atemperature at which it will flow and form a functional and secureconnection with the component. However, during this process, known asrework, the heat in the plating material can dissipate through thecircuit board or card, damaging the rest of the card and other attachedcomponents. An additional problem associated with reworking processes isthat when the heat dissipates away from the plated through hole, it isnot available to melt the plating material on the through hole.

The present invention provides a solution to the thermal managementproblems known to exist in circuit board and card rework processes.Accordingly, the present invention provides means to direct the heatgenerated by the rework process away from the components and to preventthe dissipation of heat throughout the rest of the circuit board orcard.

FIG. 1 depicts a section of a multi-layer circuit board or card 1including one of the conductive planes 2 and a plated through hole 3. Amulti-layer board such as the one depicted in FIG. 1 commonly contains anumber of such holes. The power plane 2 is just one of a number ofplanes making up the board. The power plane 2 consists of asubstantially uniform layer of some type of conductive material. Someholes in a circuit board are not plated and some do not extend throughthe entire circuit board or card. Pins may be inserted in any type ofhole.

The embodiment shown in FIG. 1 includes four thermal vents 5 locatednear the plated through hole 3 in the power plane 2. The vents 5 aresimply open areas in the power plane in which no conductive material hasbeen laid down or from which the conductive material was etched awaychemically or physically removed. Preferably, a plurality of these ventsare located throughout the power plane, surrounding every plated throughhole which will be subjected to the rework process. When a pin isinserted into the plated through hole 3 and soldered in place, the ventsact as insulators, blocking the diffusion of heat through the card. Theheat is trapped in the area adjacent to the plated through hole andensures that the plating material will reach the reflow temperature.Such an arrangement of thermal vents, as seen in FIG. 1, does notdegrade the performance of the power layer or layers in terms ofresistance and conductance.

In the embodiment of the present invention shown in FIG. 1, the platedthrough holes have a diameter of approximately 0.031 inch and 0.040inch. The center of the thermal vents is approximately 0.050 inch offsetfrom perpendicular lines passing through the center of the platedthrough hole as indicated by "d", "e", and "f". The centers of thethermal vents are approximately 0.100 inch apart as indicated by "a","b", and "c". The thermal vents themselves are approximately 0.075 inchin diameter.

FIG. 2 represents an alternative embodiment for the placement of thethermal vents in the power plane of a multi-layer circuit board or cardaccording to the present invention. The thermal vents in this embodimentare about 0.075 inch wide with centers about 0,100 inch apart asindicated by "g", "h", and "i" The thermal vents and the plated throughhole in the embodiment shown in FIG. 2 are as thick as the power plane.

The dimensions of the vents must be adequate to result in the desiredmanagement of heat. Additionally, the vents must be of adequate size todeal with the particular reflow temperature of the plating material usedon the circuit board or card. Also figuring into the determination ofthe number and size of the vents is the amount of plating material usedon the plated through holes and the thickness of the particular cardinvolved. Accordingly, the dimensions of the thermal vents are notlimited to the examples provided herein.

If the circuit board or card is particularly thick, it might bedesirable to include more and larger vents since more heat will have tobe applied to the circuit board or card to cause the reflow of platingmaterial in the center of the circuit board. Preferably, the thermalvents are not connected or attached to the power pins through a spoke.Such a spoke connection can channel the transmission of heat and mayalso cause inductance. Ssurrounding the pins the thermal vents willreduce the heat sinking capability of the power plane copper surroundingthe plated through hole connection. Regardless of which arrangement forthe vents is used, the arrangement of vents must also take intoconsideration maintaining the desired electrical characteristics of thepower plane, attached chip or other component, and the overall circuitboard or card.

FIGS. 3 and 4 represent possible arrangements for vents about particularnumbers of power pins to insure the proper management of heat away fromthe power plane. As can be seen in FIGS. 3 and 4, the vents, designated"X" in FIG. 3 and "V" in FIG. 4, generally completely surround the areain the power plane where the through holes, designated by "p", in bothfigures, for the inserted pin, are formed. The number of vents provideddepends upon the number of power pins projecting from an attachedcomponent. As seen in FIG. 4, the vents may be placed "off-grid" inrelation to the grid arrangement of the through holes. In this off-gridarrangement, the through holes are arranged in one grid and the thermalvents in a similarly spaced grid formed in the circuit board or cardsuch that each row of thermal vents is between two rows of throughholes. Similarly, each row of through holes is between two rows ofthermal vents.

Alternatively, the vents and pins may be on the same grid, as shown inFIG. 3. In the examples of through hole and thermal vent arrangementshown in FIG. 3, the through holes are arranged in groups and each groupis surrounded by thermal vents. The number of thermal vents includedabout each group of pins may vary, depending upon the thermalrequirements of the process involved. Each group of through holes may beassociated with one or more attached chips, components, or modules.

Preferably, thermal vents should be used on all "non-tied" crosssections above approximately 0.062 inch thickness. Similarly, non-tiedcross sections with thicknesses between approximately 0.040 inch andapproximately 0.062 inch and having approximately two ounce power/groundplanes should also incorporate thermal vents at isolated component pins.

In an alternative embodiment of the present invention, the thermal ventsare laid out about the plated through hole 3 so as to form a series ofsymmetrically arranged spokes 8 as seen in FIG. 5. This vent arrangementshown in FIG. 5 is preferable where multiple ties to approximately oneounce copper or greater power planes are required. Each vent in theembodiment shown in FIG. 5 preferably has a main portion 9 and anadjacent side portion 10 and 11 on either side thereof. The main portionhas edges 12 and 13 which are generally perpendicular to a diameter ofthe plated through hole the side portions and 11 are angled to followthe curvature of the pin as compared to the main portion 12. The ends 14and 15 of the side portions 10 and 11 are angled, or have a taperedshape, so that the spokes 9a preferably become wider as the distancefrom the center of the plated through hole increases.

In the embodiment shown in FIG. 5, the vents are separated from theplated through hole by at least about 0.1 mil as indicated by "j" andare typically 0.25 mil wide as indicated by "k". Such an embodimenttypically includes through holes 0.79 mil wide. In such an embodiment,the spokes are 0.2 mil thick at the point closest to the through hole asindicated by "m" and 0.29 mil at the point farthest from the throughhole as indicated by "n". The above described embodiment is only oneexample of the dimension ranges for the vents according to theembodiment of the present invention shown in FIG. 5. Preferably, thevent size is about equal to the internal clearance maximum diameter ofthe given technology and must be sufficient to provide the desiredthermal characterisitcs.

FIGS. 6 and 7 show alternative embodiments of the spoke design for thethermal vents. The embodiment shown in FIG. 7 includes only a singlespoke 109, with an inner width of approximately 0.008 inch and an outerwidth of approximately 0.014 inch. Preferably, the outer distance aroundthe spoke is about equal to the maximum clearance opening. The vent 108extends substantially around the pin and the plated through hole with asingle "flared" entry to guarantee dimensional stability duringmanufacturing and to provide the added advantage of removing the longnarrow channel electrical hit, thus reducing the added inductance or"noise" or reduction of capacitance. The vent 108 is preferablycomprised of a plurality of similarly shaped segments 109. The ends 114and 115 of the vent are angled, as in the embodiment shown in FIGS. 5and 6. However, the actual shape of the vent may vary. For instance, thevent may be a smooth rounded shape.

Preferably, each spoke as seen in FIG. 5 is about 0.0098 inch wide fromthe edge closest to the pin to the edge farthest from the pin. The edges14 and 15 of the side portions 10 and 11 preferably are angled such thatthe edges of the two adjacent vents are about 0.0079 inch apart at thepoint closest to the pin and about 0.0114 inch apart at the pointfarthest from the pin. Therefore, the spoke is about 0.0079 inch wide ata point closest to the pin and about 0.0114 inch wide at a pointfarthest from the pin. Preferably, the vents are arranged so that theyare at a minimum of approximately 0.010 inch from the edge of the platedthrough hole. An increase in the slope of the angle between the vents,and, hence, an increase in the width of the spoke as the distance awayfrom the pin increases, reduces inductance caused by the long narrowchannel. This increasing spoke width with increasing distance from thethrough hole provides the maximum thermal area with only one neck downrestricting capacitance.

Due to the fact that the spoke design shown in FIG. 5 is made ofindividual line segments, it can be line drawn in automatic mode ofgeneration thereby reducing costs, time, and expense. On the other hand,the standard thermal break design must be flashed through and includesuse of a polygon and can not be automated.

The vent design shown in FIG. 5 can be seen in cross section in FIG. 8.The vent design shown in FIGS. 5-7 is preferably used in an enhancedthermal break design shown in FIG. 8 in which some of the power planesare provided with vents and some include a solid connection completelyabout the plated through hole. To achieve optimum AC and DC powerdistribution, it is desirable to tie common multiple ground planestogether at each ground pin location as well as at each voltage pinlocation. In the embodiment shown in FIG. 8, to ensure that more than50% of the plated through hole is filled with solder during rework, theconnection to the plane should be solid as indicated by the solidconnection 16 with the power plane extending all the way to the platingon the plated through hole. To ensure that more than 50% of the platedthrough hole is filled with solder during rework, the circuit board orcard may also include an improved thermal brake design, including thevents shown in cross section in FIG. 5. With this design, seriesinductance and resistance from the component 20 to the closest groundplane G1 in FIG. 8 is unchanged by the thermal breaks at the remainingground planes G2 and G3. Table 1 presents differences in variouselectrical parameters comparing a plated through hole about which eitherfour spokes as seen in FIG. 5 or two spokes are included in the thermalmass design.

                  TABLE 1                                                         ______________________________________                                        Improved Thermal Break Design-Electrical Parameters                                           Four Spokes                                                                              Two Spokes                                         ______________________________________                                        Self-Inductance (nH)                                                                          0.018      0.035                                              Resistance (mohm)                                                                             0.2        0.3                                                Maximum Current depends upon                                                                             depends upon                                                       application                                                                              application                                        ______________________________________                                    

As seen in FIG. 8, a circuit board or card may include thermal vents 18,signal planes 16a, ground planes 16b, and voltage planes 16c. The cardin the embodiment shown in FIG. 8 is approximately 0.055 inch thick andincludes an approximately 0.040 inch plated through hole. The pin 19 isinserted into the hole and typically extends above the surface of thecard about 0.06 inch and is about 0.028 inch in diameter. The exampleseen in FIG. 8 includes the desired greater than about 50% solder fill21.

As seen above in Table 1, the design of the thermal break can effect thefunctional parameters of the card. To determine the significance of thethermal break inductance on functionality and performance, other powerdistribution inductance that is occurring in series with the thermalbreaks must be considered. As an example, Table 2 shows the increase inseries inductance due to the addition of a thermal break when added inseries with a typical component/connector pin.

                  TABLE 2                                                         ______________________________________                                        Module/Connector Pin Comparison-                                              With/Without Thermal Break                                                                    Con Pin +          Con Pin +                                           Con Pin                                                                              Break     Con Pin  Break                                      ______________________________________                                        Self-Inductance                                                                          10.59    10.63     10.59  10.63                                    (nH)                                                                          Loop-Inductance                                                                          13.06    13.13     13.06  13.13                                    (nH)                                                                          ______________________________________                                    

The data in Table 2 reflects the worse case performance scenario inwhich two spokes of the thermal break are missing and/or open. In thissituation, the self inductance increase due to the thermal break is lessthan about 6% in the lower planes. If, inductances of modular/chip powerbusses and card L/square were considered, the percentage increase ininductance due to the thermal break would be much lower. To ensure thatthe inductance to the power system is minimized, power vias can be addedin the vicinity of thermal breaks to provide low inductance commonpoints for ground or voltage. A power via is a plated through hole whichis not associated with any component pins and which has solidconnections at all ground (power) planes.

The values in Table 2 were determined using a module with a pinapproximately 0.028 inch in diameter in an approximately 0.040 inchplated through hole with a typical card stand off of approximately 0.060inch and an overall card thickness of approximately 0.060 inch. Theconnector pin numbers were determined using an approximately 0.020 inchdiameter pin with an approximately 0.053 pin length. The loop inductancevalues assume one return circuit pin about 0.100 inch away, with theloop consisting of pin 1--thermal break 1--solid copper plane thermalbreak 2--pin 2. The thermal break values assume that two spokes aremissing.

If the geometry of the circuit board or card does not allow for thermalbreaks or the other vent configurations described above, single powerpickups may be necessary to guarantee assembly/rework. This isespecially true with cards using increased amounts of copper, thereforecreating a greater thermal mass than was previously known and also dueto the utilization of double and triple ties on the power and groundplanes. To overcome these problems, the present invention also providesa "thermal tied power net" as described below.

As seen in cross section in FIG. 9, the plated through holes and, hence,pins extending from the components into the plated through holes areconnected only to certain of the power planes. The space between theplanes and the through hole may be a standard power clearance hole,depending upon the technology involved in the application of the circuitboard or card. If a through hole is only connected to one plane, theheat generated during rework cannot flow to the other planes. The powerplanes are tied together with a power via. The thermal net eliminatesthe need to achieve reflow of the plating material in the through hole.The thermal mass occurs at the tie via's, away from the component.

In the embodiment shown in FIG. 9, the pins inserted into the platedthrough holes are tied to alternate planes. The first pin 26 is tied tothe first power plane 27 the second pin 27 is tied to the second powerplane 28 and the third pin 29 is tied to the first ground plane 30 whilethe fourth pin 31 is tied to the second ground plane 32. The first powervia 33 is used to tie the first power plane 27 and the second powerplane 28. The second power via 34 is used to connect the ground planes30 and 32. The power vias 33 and 34 should be located in the card asclose to the component as possible to provide common in between thepower and ground planes.

Using the alternative embodiment of the thermal net design as seen inFIG. 10, the pins 22 of the component 23 are tied to a single plane 24.Non-functional tie vias 25 are used to tie either common power planes orcommon ground planes together. The embodiment shown in FIG. 10 includesdouble tie vias connected to two power planes. The power vias used totie the ground planes are non-functional and in the embodiment shown inFIG. 10 are approximately 0,016 inch or greater, depending on thethermal function required. The non-functional power vias may be set in anet, interstitial of off grid.

The tie vias in FIGS. 9 and 10 may be used to tie either the power orground planes. An advantage of these tie vias is that the thermal massis concentrated at the tie vias rather than in the plated through hole,thereby concentrating the thermal mass away from the plated throughhole. By removing the direct tie from near the plated through hole, useof the tie vias removes solder fill and rework problems associated withdirect tie occurring at the plated through hole. The use of a net ofvias ensures a short distance to the ties. Further, the tie vias requireno hole fill or rework thereby eliminating the problems associated withconcentrating heat at the plated through hole to melt solder to createhole fill 21. Since the via is not functional to the component, this iswhat is meant by non-functional, it removes the tie from rework unlikeother embodiments in which the functional pins from the component areinserted throughout the plated through hole requiring solder flow tooccur along the entire length of the plated through hole.

From a power distribution perspective, it is preferable that ground orpower plane pickups alternate pin by pin rather than assigning allground or power pins of a component to one plane. The advantagesprovided by alternating pickups among planes include the fact thatalternate pickups take advantage of all plane-to-plane capacitancesbetween ground or power plane pickups to reduce Delta-I noise. Delta-Inoise is the inductive noise in a power distribution system created as alarge number of drivers on a chip are turned on and is defined as (thechange in current per unit of time)×(power inductance). Also, an equalcurrent distribution among like planes is encouraged. Additionally,alternating pickups among planes provides a redundancy of planecommoning at many component sites (module/chip power buses) in additionto at the power vias. Further, alternating pickups result in the lowestinductance power distribution system due to advantage of mutualinductances of interleaved planes. Still further, alternating pickupsestablishes a better AC reference for off-module signal communication.Component-by-component assignment would more likely result inmodule-module AC reference differences due to Delta-I induced voltagetransients. The addition of power vias in close proximity to singlepower pickups will partially compensate for the increased powerdistribution impedance seen by the component. It is recommended that onepower via be added as close as possible to each single power tie tocommon like planes.

As seen in FIG. 9, by alternating the power and ground plane pickups toalternate pins-by-pin connections, rather than assigning all ground orpower pins of a component to one plane, all plane to plane capacitancesbetween power and ground planes are taken advantage of to reduce Delta-Inoise. Also, such a pin to plane connection arrangement promotes equalcurrent distribution among like planes. Further, a redundancy of planecommuning occurs at many component sites such as module/chip powerbuses. Additionally, such alternating pin connections result in thelowest inductance power distribution due to the advantage of mutualinductances of interleaved planes. A better AC reference for off-modulesignal communication is also established by alternating pin placement.On the other hand, a component by component assignment would more likelyresult in module-module AC reference differences due to Delta-I inducedvoltage transients. In such an arrangement, the addition of power viasin close proximity to single power pickup will partially compensate forthe increased power distribution impedance seen by the component. It isalso recommended that one power via be added as close as possible toeach single power tie to common like planes.

To further control the dissipation of heat through a circuit board orcard, as seen in FIG. 11, thermal vents and/or heat trap vias may belocated about the periphery of large modules such as TCM, SBC and cardedge power components, and others having ground and/or power pins inremote corners. The heat traps and thermal vents localize the heatwithin the module site to minimize reflow of adjacent components. Notonly do the thermal vents and heat trap vias prevent the flow of heat toadjacent components, they trap the heat next to the module therebyallowing corner power pins to heat up to reflow more evenly with signalpins located away from the periphery of the component thereby allowing areduction of the number of heat cycles and reducing card stress.Further, confined heat made possible by the heat traps and thermal ventsreduces heat dispersion to adjacent components reducing reflow toadjacent sites.

As seen in FIGS. 11-13, the module 35 includes inboard ground pins 36.Signal or voltage pins 37 include clearance lands 38. As in theembodiment shown in FIG. 11, the signal and voltage pins with theclearance lands act as thermal vents for the in board groundconnections. However, due to their location about the periphery, groundpins at the corners 39 are not adjacent on all sides to such signal orvoltage pins with clearance lands. Therefore, to reduce heat flow toadjacent components, thermal vents or heat trap vias 40 are added to thecard about the edge of the component or module. As seen in FIG. 12,these thermal or heat trap vias may be added about all corners of themodule. The inductance seen by the corner ground pins with thermal ventsor heat trap vias is equal to or less than inboard ground pinssurrounded by signal or voltage pins with clearance lands. Since theclearance holes created by the thermal vents or heat trap vias arecomparable in diameter and on the grid lines as those holes existing inthe interior of the module, the power distribution perimeters (L/square,R/square) seen by the corner pin will be the same as the existing modulearea.

FIG. 13 shows a close up cross section of a heat trap via 40 adjacent toa corner ground pin of the module. The squiggly lines represent the flowof heat created during rework as it flows from the areas interior to themodule and is redirected by the thermal vents and/or heat trap vias backtoward the plated through hole, where it will help to melt the solder orplating material. Therefore, the heat is prevented from dissipating intothe rest of the card where it may damage the card and/or attachedcomponents, helping to ensure that complete solder fill is more likelyto occur. The attached component 35 has attached pins 35a inserted intothe plated through hole.

FIG. 14 shows a perspective view of a component to be attached to acircuit board or card including at least some of the improved thermalmass designs of the present invention. The component 50 includesalternating power pickups from a single pad thereby reducing inductanceto the power or ground plane. The pad 50a in the embodiment shown inFIG. 14 is about 120×60 mils. The extent to which inductance is reduceddepends upon the application involved.

Such a module as shown in FIG. 14 may be used with a circuit card orboard including 0.012 mil via's on a 25 mil grid. According to theinvention, a 25 mil grid may be offset from the straight grid single tieby about 50 mil. Also, a 25 mil grid may be interstitial to allowalternate pick-up. This arrangement is demonstrated in the embodimentshown in FIG. 14, where the pick-ups 50b and 50c are about 50 milsapart. The pick-up 50d is about centered between the two pickups 50b and50c and its center is about 25 mils away from a line passing through thecenter of the pick-ups 50b and 50c.

In the prior art, depicted in FIG. 14a, it was common to tie all threeplanes with a single triple tie. However, this method results in thermalmass problems. Therefore, the embodiment shown in FIG. 14 in which eachplane is connected to a separate tie was developed. The module may beused with any of the various embodiments of the present inventiondescribed in detail above.

As seen in FIGS. 15a-e, some examples of various configurations of amulti-layer circuit board or card present different problems requiringdifferent solutions for managing thermal conditions within the circuitboard or card according to various embodiments of the present invention.The examples shown in FIGS. 15a-e are illustrative and do not includeall possible plane and thermal mass designs according to the presentinvention. The design used to accomplish thermal management depends uponthe specifics of the circuit board or card cross section, component typeto be reworked, and the number of voltage or ground planes that it isdesired to common at each power pin. The options include, for example,thermal vents, heat trap vias, solid connections to the top power orground plane with improved thermal break design at all remaining planeconnections with supplemental power vias recommended to common likeplanes, and single power pickups with alternating plane assignments withsupplemental power vias to common like planes.

The embodiment shown in FIG. 15a includes finished circuit board or cardthickness of between about 0.040" and about 0.062", with layers V1, V2,G1, and G2 all including 0.5 ounce material. The ounce measurement forthe material defines the amount of material that is present perapproximately one square foot of about 0.0014" thick of that material.For the embodiment shown in FIG. 15a, thermal vents at the power pickupscould be used if the carrier thickness exceeds about 0.062". Theembodiment shown in FIG. 15c, the planes V1, G1, V2, and G2 include 1.0ounce material and a thickness of between about 0.040" and about 0.062"

In the embodiment shown in FIG. 15c, one ground plane and one voltageplane are provided which are made of 2.0 ounce material. The card has athickness of between about 0.040" and about 0.062. In this case, ventsmay be provided at power/ground pickups.

The embodiment shown in FIG. 15d includes three ground planes, G1, G2,and G3, and three voltage planes, V1, V2, and V3. The planes may be 0.5oz., 1.0 oz., or 2.0 oz. or any mix thereof, utilizing multiple ties.The circuit board may be between about 0.062" and about 0.090" inthickness and above. In such an embodiment, thermal breaks may beprovided on all ties, except for solid connections at the top voltageand ground planes. These thermal breaks are combined with a power netfor even power distribution. FIG. 15d shows that as layeredcross-section thickness increases, the same symmetry should bemaintained with solid connection on the uppermost layers.

In FIG. 15e, thermal net with power vias may be used. The embodimentincludes a voltage plane and a ground plane and off grid/interstitial<100 mils on connectors/high density modules. If a grid is interstitial,it is physically impossible to vent or break based upon a of geometricspace. In such a situation, as illustrated in FIG. 16, if vents wereplaced about the through holes, they would overlap. In FIG. 16, thedotted lines about the through holes represent where vents or breakswould extend to if they were included. Such a card could not physicallyexist since so much material would be lacking from the circuit board orcard. Therefore, single ties and ties into a remote via outside the gridarray must be used, as shown about the periphery of the grid in FIG. 16.

By employing the present invention for thermal design into the structureof circuit boards and cards, a significant savings is realized ascompared to using prior art techniques for designing and constructingcircuit boards and cards. The present invention allows a great decreasein the number of circuit boards and cards which are lost during reworkand the number which are lost to scrap. Savings are also achieved intime, energy and materials since fewer boards or cards need to bereworked due to proper connections not being formed due to adequatesolder temperature not being achieved.

Regarding the prior art, the present invention also provides theunexpected result of reducing inductance while also allowing thermalabatement. This is at least in part due to the design of the presentinvention, especially as seen in FIG. 5, with spokes that vary in width,increasing in width as the distance from the pin increases. The presentinvention is especially useful with high performance packages that arehighly sensitive to noise. In prior art thermal designs which

The present invention may also be used for laminates of higherperformance and higher density with maximum card thickness with multiplecommon ties of up to seven ounces of copper used in a process. Someactive components can not be used in an immersion process, since theyhave a solder hierarchy that would reflow when chips are attached in animmersion state. Therefore, the present invention is also designed inthe Z-axis as to a common reference to a top plane.

We claim:
 1. A multi-layer printed circuit board or card including aplurality of conductive planes, including ground and power planes, andinsulating planes, said circuit board or card having a plurality ofthrough holes formed through at least one of said planes, said throughholes having an electrically conductive material plated onto the insidesurface, at least one integrated chip or component being attached tosaid circuit board or card such that pins made of an electricallyconductive material and attached to a surface of said chip or componentextend into said plated through holes, said circuit board or cardcomprising:at least one thermal relief passage in at least one of saidplanes for preventing the diffusion of heat throughout said circuitboard or card during the securing or removal of said pins in said platedthrough holes by the heating of said plating material to a temperatureabove a melting point of the plating material, said at least one thermalrelief passage located in the vicinity of at least one of said platedthrough holes and being free from connection with said pins.
 2. Themulti-layer printed circuit board or card according to claim 1, whereinsaid at least one thermal relief passage is a thermal vent formed in atleast one of said conductive planes, said thermal vent being a hollowopening in said at least one conductive plane and being formed in thevicinity of at least one of said plated through holes.
 3. Themulti-layer printed circuit board or card according to claim 1, furthercomprising a plurality of said thermal relief passages symmetricallylocated in the vicinity of and about at least one of said plated throughholes.
 4. The multi-layer printed circuit board or card according toclaim 3, wherein said thermal relief passages are thermal vents.
 5. Themulti-layer, printed circuit board or card according to claim 4, whereina space between adjacent thermal vents is in the form of a spoke, saidspoke increasing in width as the distance from the plated through holesincreases.
 6. The multi-layer printed circuit board or card according toclaim 3, wherein four circular thermal vents are located in the vicinityof each of said plated through holes.
 7. The multi-layer printed circuitboard or card according to claim 6, wherein the center of each of saidthermal vents is located about 0.050 inch away from a straight linepassing through the center of said plated through hole and the center ofadjacent thermal vents is about 0.100 inch from the center of theadjacent thermal vents.
 8. The multi-layer printed circuit board or cardaccording to claim 4, wherein each conductive plane in said multi-planecircuit board or card includes said thermal vents adjacent said platedthrough holes.
 9. The multi-layer printed circuit board or cardaccording to claim 4, wherein said thermal vents extend entirely througheach of said conductive planes.
 10. A multi-layer printed circuit boardor card according to claim 2, wherein a space between opposite ends ofsaid at least one thermal vent is in the form of a spoke, said spokeincreasing in width with increasing distance away from the at least oneplated through hole.
 11. The multi-layer printed circuit board or cardaccording to claim 10, wherein said at least one vent is eight sided,with a first side parallel to a straight line passing through the centerof said plated through hole; a second side parallel to said first side,said first side being closer to said plated through hole; third andforth sides connected to opposite ends of said first side, said thirdand fourth sides extending from opposite ends of said first side at anacute angle toward said through hole; fourth and fifth sides extendingfrom opposite ends of said second side parallel and being to said thirdand fourth sides; seventh and eighth sides connecting said third andfourth sides with said fifth and sixth sides and being angled toward thecenter of said vent with increasing distance from said through hole. 12.The multi-layer printed circuit board or card according to claim 10,wherein said at least one thermal vent extends substantially around oneof said plated through holes, said spoke including a plurality ofsubstantially straight segments and wherein said spoke is defined by theends of the one spoke.
 13. The multi-layer printed circuit board or cardaccording to claim 2, wherein said circuit board includes thermal ventsselectively formed in ground planes in said multi-layer circuit board orcard, such that a first ground plane closest to said attached chip orcomponent on said circuit board or card does not include thermal ventsin the vicinity of said plated through holes and ground planes furtherfrom said attached chip or component include said thermal vents in thevicinity of said plated through holes.
 14. The multi-layer printedcircuit board or card according to claim 1, wherein:said attachedcomponent or chip is a module, said module including a plurality ofcomponents attached thereto; said conductive planes are selectivelyfunctionally connected to said plated through holes; and said at leastone thermal relief passage is formed about the perimeter of the moduleand extends through the entire length of said circuit board or card, andis plated on an inside surface with an electrically conductive material,and is connected either to all of said ground planes or said powerplanes.
 15. The multi-layer printed circuit board or card according toclaim 1, wherein said at least one thermal relief passage is formedabout the perimeter of the chip or component, and extends through theentire length of said circuit board or card.
 16. The multi-layer printedcircuit board or card according to claim 15, wherein said circuit boardor card also includes thermal vents formed about the plated throughholes formed where the pins extend from the chip or component into theplated through holes.
 17. The multi-layer printed circuit board or cardaccording to claim 15, wherein the pins attached to said chip orcomponent are of various lengths and are selectively attached to saidpower plane and ground planes.
 18. The multi-layer printed circuit boardor card according to claim 1, wherein said board or card includes aplurality of said passages, said passages being thermal vents andsurrounding at least one of said plated through holes, said through holeand said thermal vents being co-linear.
 19. The multi-layer printedcircuit board or card according to claim 1, wherein said board or cardincludes alternating rows of said plated through holes and pluralthermal relief passage formed in at least one of said conductive planes,said rows of through holes being between said rows of thermal reliefpassages and said rows of thermal relief passages being between saidrows of through holes.